Radiometric aircraft landing system

ABSTRACT

An aircraft landing system employing passive radiometer apparatus mounted in an aircraft to scan a specially arranged ground target, which will provide directional and altitude guidance in the vicinity of an airfield. The ground target extends along the desired flight path and is designed to cause large differences between horizontally and vertically polarized radiometric noise, easily detected and analyzed by the radiometer. Portions of the ground target may have augmented noise sources in specific patterns, for marking and identification purposes. The radiometer output can provide visual or audible aid to manual control, or be used to operate an automatic pilot, or the like.

United @tates Patent Killian et al. [45] July 25, 1972 [54] RADIOIVETRICAIRCRAFT LANDING SYSTEM Primary Examiner-Benjamin A. Borchelt AssistantExaminer-Richard E. Berger [72] Inventors Damn? i Frank Jame both ofAttorney-Carl R. Brown, Stephen L. King and Kenneth W.

San Diego, Calif. M at 6 er 4 [73] Assignee: Teledyne Ryan AeronauticalCompany,

San Diego, Calif. [57] ABSTRACT [22] Filed: Oct. 12, 1970 An aircraftlanding system employing passive radiometer ap- 21 A L N 79 894 paratusmounted in an aircraft to scan a specially arranged pp ground target,which will provide directional and altitude guidance in the vicinity ofan airfield. The ground target ex- U-S. ME, LS, R tends along thedesired path and is designed to cause [51] Int. Cl ..G0lw 1/00 largediff between horizontally and vertically polarized [58] Field of Search..343/100 ME, 100 PE, 108 R, radiometric noise7 easily detected andanalyzed by the 343/ LS radiometer. Portions of the ground target mayhave augmented noise sources in specific patterns, for marking and [56]References cued identification purposes. The radiometer output canprovide UNITED STATES PATENTS visual or audible aid to manual control,or be used to operate an automatic pilot, or the like. 2,458,654 1/1949Southworth ..343/100 ME X 2,502,974 4/1950 McElhannon ..343/108 R 10Claims, 6 Drawing Figures 38 32 34 3O l E R R0 R 42 44 45 OUTPUTTRACKING igg g? AMPLIFIER PHASE T w I ANTE NNA RECEIVE R REFERENCEDISCRIMINATOR AMPLIFIER A OUTPUT 52 47 AMPLIFIER 36 V 40 REQUIREDALTITUDE INHIBIT INPUT 4B 58 ABSOLUT E ALTITUDE ALTITUDE Q JIK SIGNALERROR REFEREfigE COMPARATORT AMPLIFIER T0 DISTANCE TO 50 54 57 TOUCHDowN INDICATOR TO AUTOMATlC NAVIGATION SYSTEM PATTENEFEDIIMS I9723,680,111

32 34 3O ERROR 42 44 4 oUTPUT h RADIOMETER AMPLIFIER TRACK'NG TRACKINGPHASE $35553 ANTE NNA DISCRIMINATOR AMPLIFIER RECEIVER REFERENCE OUTPUT52 47 A AMPLIFIER 36 40/ REQUIRED ALTITUDE INHIBIT INPUT 48 56 fiifigg;A LT l TU DE ALTITUDE AGE SIGNAL ERROR 'g' -g COMPARATOR K AMPLIFIER T0DISTANCE T0 50 54 57 TOUCH-DOWN INDIcAToR TO AUTOMATIC NAVIGATION ISYSTEM I/IJU D If I-IMHNF'ZINHNHI'IWHHHTF-LP Fig. 2

W W I T\ O Fig.4

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INVENTORS DERLING G. KILLION FRANK J. JANZA Y @MM ATTORNEY RADIOMETRICAIRCRAFT LANDING SYSTEM BACKGROUND OF THE INVENTION Landing aid systemsfor aircraft usually involve a guiding beam transmitted from groundbased apparatus from precise alignment with the runway. The aircraftcarries receiving equipment compatible with the ground basedtransmitter, and deviations of the aircraft from the prescribed flightpath are indicated by changes in characteristics of the receivedsignals. The ground based transmitter capable of producing suitablesignals is complex and expensive and requires careful installation andfrequent maintenance. As a result, such apparatus is not usually foundat small airfields or temporary landing strips, where the aid would bevaluable. Further, since several different types of beam guidancelanding aids are in present use, an aircraft must carry receiving meanscompatible with each type to be operable at many different locations.

An ideal system would have one simple type of apparatus carried by anaircraft, compatible with ground based means which is easily installedto suit a specific location, requires no power supply and almost nomaintenance.

SUMMARY OF THE INVENTION The aircraft landing system described hereinutilizes a passive ground target assembly in the form of a conductivegrating, designed to provide a large difference between horizontally andvertically polarized radiometric noise. In the aircraft, a passivescanning radiometer detects the noise from the ground target andanalyzes the results to provide directional and altitude data. Theconductive grating extends along the required flight path to the runwayand may take the form of metals slats or rods secured just above theground surface on individual or common supports. In a very simple formthe slats can be metallized strips on a non-conductive backing strip,such as Mylar or other suitable plastic, which is easily spread inposition and can be rolled up after use for a temporary landing strip.

Patterns or characters can be incorporated in the ground target, byvarying the grating or by means of noise augmenting elements, such aslamps, between the slats. Specific characters can be read by a suitableradiometer and can serve as identification or position markers. Thesystem is adaptable to radio frequency, infrared, or other radiometricfrequency bands.

The primary object of this invention, therefore, is to provide a new andimproved radiometric aircraft landing system.

Another object of this invention is to provide an aircraft landingsystem, in which a simple passive radiometer unit carried in an aircraftis compatible with a variety of ground targets or markers.

Another object of this invention is to provide an aircraft landingsystem in which the ground target is essentially passive and is easilyinstalled in a permanent or temporary manner in any desired location.

A further object of this invention is to provide an aircraft landingsystem which is adaptable to substantially all existing aircraft andlanding fields, without interfering with operation of the aircraft orother facilities.

Other objects and many advantages of this invention will become moreapparent upon a reading of the following detailed description and anexamination of the drawings, wherein like reference numerals designatelike parts throughout and in which.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of theairborne radiometer apparatus.

FIG. 2 is a diagrammatic plan view of a typical ground tar- DESCRIPTIONOF THE PREFERRED EMBODIMENT The basic ground target 10, shown in FIG. 2,is an elongated grating composed of parallel conductive slats l2 spacedalong a flight path indicated by broken line 14, which leads to a runway16. Slats 12 are substantially parallel to the ground surface andperpendicular to the flight path 14. The slats are spaced slightly abovethe ground, either on posts 18, as in FIG. 4, or on common rails orother suitable supporting means. As shown the slats are flat metalstrips or bars, but could be round rods, or of other cross sections. Thespacing between the slats 12, indicated at A in FIG. 3, should be lessthan one half wavelength of the operating frequency of the radiometerbeing used, otherwise the dimensions are not particularly critical.

An alternative, very simple form of target is shown in FIG. 5, in whichslats 20 are in the form of metallized strips on a backing sheet 22 ofplastic material, such as Mylar or other weather and wear resistantmaterial. In this form the target can be put in placed quickly for atemporary landing strip and rolled up after use.

A further form, shown in FIG. 6, is a grating type structure, with slats24 joined by longitudinal members 26, which can be a unitary structureor built up. The spacing A between slats 24 is less than one halfwavelength, but the spacing B between members 26 must be more than onehalf wavelength in order to provide the necessary polarization.

The airborne radiometer, shown in block diagram form in FIG. 1, is apassive unit which detects radiometric noise given ofi by virtually allsurfaces and objects, the emissivity being a function of the dielectricconstant and surface condition of the objects. Radiometric noise coversa very broad spectrum and the radiometer is tuned to respond to aparticular frequency band, specifically in the microwave region, theslat spacing of the ground target being made compatible.

The radiometer includes a tracking antenna 30, which may be aconventional monopulse or a conical scanning type, pointed toward thenadir feeding input signals to a receiver 32. The input signalsrepresent the horizontally and vertically polarized radiometric noiseand the receiver contains integrating circuitry which provides adifference output 34 and a sum output 36, the technique and circuitrybeing well known. Output 34 is amplified in an amplifier 38 to provide auseable error signal, and output 36 is amplified in an amplifier 40 toprovide a reference signal which represents the total radiometric noisereceived. Both amplified signals are fed to a phase discriminator 42,the output 44 of which is a turn signal, indicating deviation of theaircraft from flight path 14. The output 44 is fed through an amplifier46 to the existing autopilot or automatic navigation system in theaircraft, fordirectional correction of the course. Conventional visualturn indicating means 47 may be used in addition to or instead of theconnection to an autopilot, to aid manual control of the aircraft.

Sum output 36 provides an absolute altitude voltage reference 48,representing actual altitude of the aircraft above the terrain. This isapplied to a comparator 50, together with a required altitude inputvoltage 52, which is preset to suit the approach characteristics of theparticular airfield. The output of comparator 50 is an altitude errorsignal 54, which is amplified by an amplifier 56 and fed to theautomatic navigation system, or to a suitable visual display 57. With anavigation or autopilot system having descent rate and glide pathcontrol, the altitude reference 48 can be applied to the existingdistance to touch-down indicator. To avoid unnecessary altitudecorrections, an inhibiting circuit 58 is connected between the turnsignal output 44 and altitude error amplifier 56, to inhibit an altitudeerror signal output unless the turn signal output is zero. Thus thealtitude is corrected only when the aircraft is on the flight path.

The various components of the radiometer apparatus are all well knownand will vary in circuitry according to the frequencies involved. Forsome purposes an infrared system is practical, but a radar or microwavesystem may be more desirable for its all-weather capability.

In operation, the vertically polarized radiation, indicated bydirectional arrow 60 in FIG. 3, is reflected from the grating and iseffectively the same as the sky noise temperature, about 135 K. Thehorizontally polarized radiation, represented by arrow 62, passesthrough the grating and assumes the ground noise temperature, about 300K. With a difference ratio of more than 2 to 1, the system is operablewith a completely passive ground target.

Since the radiometer can be designed with good resolutioncharacteristics, contrasting noise areas in specific configurations,such as geometric shapes or alphanumeric characters can be recognized.An oscilloscope type display coupled to the radiometer will provide avisual representation of the noise pattern in some detail. Artificialnoise sources 64 may thus be placed between slats 12 in specificpatterns, typified by the solid square 66 and hollow square 68 in FIG.2. The noise sources may be neon or fluorescent lamps, which have plasmaradiation detectable by aradiometer. Such augmented noise sources couldbe used to identify an airfield, or for position markers. in the latteruse the effective noise temperature may be selected to provide aspecific altitude reference signal to the radiometer at a particularmarker, which is an aid in maintaining a proper descent path. While thistechnique adds active components to the ground target, lamps requirelittle maintenance compared to radio beacons, and characters or symbolsare easily changed by selecting different lamps in an array.

The system is thus adaptable to automatic or semi-automatic landingtechniques, or as an aid to manual control. Ground targets can beconstructed at low cost and are easily set up to facilitate the use of asingle type of airborne radiometer unit at any location.

We claim:

1. A radiometric aircraft landing system, comprising:

a radiometer for installation in an aircraft and having an antenna withmeans for scanning the ground along the flight path;

a ground target extending along the predetermined flight path to alanding strip, said ground target having radiometric noise polarizingelements arranged to provide a high contrast between horizontally andvertically polarized noise relative to the flight path;

said radiometer having a receiver with means to compare the horizontallyand vertically polarized noise signals and provide a difference output,and a sum output representing total noise received;

discriminator means connected to said difference and sum outputs andproviding a turn error signal;

a source of altitude signal representing required altitude;

comparator means connected to said source and to said sum output andproviding an altitude error signal;

and means for utilizing said turn and altitude error signals for controlof an aircraft.

2. A radiometric aircraft landing system according to claim 1, andincluding inhibiting means responsive to said turn error signal toinhibit the altitude error signal when a turn error signal is present.

3. A radiometric aircraft landing system according to claim 1, whereinsaid ground target comprises a plurality of conductive slat elementsspaced along and substantially perpendicular to the flight path.

4. A radiometric aircraft landing system according to claim 3, whereinthe spacing between adjacent slat elements is less than one halfwavelength of the effective radiometer frequency.

5. A radiometric aircraft landing system according to claim 4, whereinsaid slat elements are spaced above and substantially parallel to theground surface.

6. A radiometric aircraft landing system according to claim 4, andincluding radiometric noise augmenting elements between certain of saidslat elements.

7. A radiometric aircraft landing system according to claim 6, whereinsaid noise augmenting elements are arranged in specific patterns.

8. A radiometric aircraft landing system according to claim 6, whereinsaid noise augmenting sources are electric lamps.

9. A radiometric aircraft landing system according to claim 1, whereinsaid ground target comprises a flexible backing sheet transparent toradiometric noise and having a plurality of metallic slat elementsthereon in spaced parallel relation along and substantiallyperpendicular to the flight path.

10. A radiometric aircraft landing system according to claim 1, whereinsaid ground target comprises a conductive grid having slat elements inspaced parallel relation along and substantially perpendicular to theflight path at a spacing of less than one half wavelength of theeffective radiometer frequency, and longitudinal members interconnectingsaid slat elements with a spacing greater than one half wavelength ofthe effective radiometer frequency.

1. A radiometric aircraft landing system, comprising: a radiometer forinstallation in an aircraft and having an antenna with means forscanning the ground along the flight path; a ground target extendingalong the predetermined flight path to a landing strip, said groundtarget having radiometric noise polarizing elements arranged to providea high contrast between horizontally and vertically polarized noiserelative to the flight path; said radiometer having a receiver withmeans to compare the horizontally and vertically polarized noise signalsand provide a difference output, and a sum output representing totalnoise received; discriminator means connected to said difference and sumoutputs and providing a tuRn error signal; a source of altitude signalrepresenting required altitude; comparator means connected to saidsource and to said sum output and providing an altitude error signal;and means for utilizing said turn and altitude error signals for controlof an aircraft.
 2. A radiometric aircraft landing system according toclaim 1, and including inhibiting means responsive to said turn errorsignal to inhibit the altitude error signal when a turn error signal ispresent.
 3. A radiometric aircraft landing system according to claim 1,wherein said ground target comprises a plurality of conductive slatelements spaced along and substantially perpendicular to the flightpath.
 4. A radiometric aircraft landing system according to claim 3,wherein the spacing between adjacent slat elements is less than one halfwavelength of the effective radiometer frequency.
 5. A radiometricaircraft landing system according to claim 4, wherein said slat elementsare spaced above and substantially parallel to the ground surface.
 6. Aradiometric aircraft landing system according to claim 4, and includingradiometric noise augmenting elements between certain of said slatelements.
 7. A radiometric aircraft landing system according to claim 6,wherein said noise augmenting elements are arranged in specificpatterns.
 8. A radiometric aircraft landing system according to claim 6,wherein said noise augmenting sources are electric lamps.
 9. Aradiometric aircraft landing system according to claim 1, wherein saidground target comprises a flexible backing sheet transparent toradiometric noise and having a plurality of metallic slat elementsthereon in spaced parallel relation along and substantiallyperpendicular to the flight path.
 10. A radiometric aircraft landingsystem according to claim 1, wherein said ground target comprises aconductive grid having slat elements in spaced parallel relation alongand substantially perpendicular to the flight path at a spacing of lessthan one half wavelength of the effective radiometer frequency, andlongitudinal members interconnecting said slat elements with a spacinggreater than one half wavelength of the effective radiometer frequency.